The invention relates to a calibration method for evaluating spectra of a spectrometer for examining solid, liquid or gaseous substances.
This calibration method involves the analysis of spectra produced by way of a spectrometer. Such analysis methods and devices function according to the principle whereby a transmitter emits electromagnetic radiation onto the substance to be examined and those rays which are reflected by or penetrate through the substance are recorded by a receiver. For these examinations all wavelength regions of the electromagnetic spectrum may be used. Particularly suitable is the wave region in the near infra-red (NIR). Such methods and devices are among those mentioned in CH 685807 A5 or CH 683713 A5.
This analysis method is applied in particular in the pharmaceutical, chemical, cosmetic, colouring, plastics, rubber and foodstuffs industries.
Since with this spectral method there are various instrument types, sensors, substance types, aggregate conditions, mathematical methods and calibration behaviour and for each substance to be examined there are nominal spectra, calibration is required before the actual evaluation.
Until now the calibration was effected by time-consuming, empirical, intuitive or xe2x80x9cguessingxe2x80x9d determination of the required variables cited above.
The object of the present invention is to specify a calibration method which automatically in as short a time as possible ascertains the optimal boundary conditions of the actual evaluation method.
According to the invention this object is achieved by the method described below, wherein the calibration is effected automatically.
Furthermore with the calibration method according to the invention the structure of a knowledge base which contains all data, expert knowledge, and their weightings may be developed.
For calibration further there serve the nominal spectra known for a substance to be examined.
The measured spectra are generally characterised by a multitude of oscillation superpositions. A visual evaluation is therefore practically not possible. Specific differences in the spectra of similar substances often consist only of a slight displacement or small shape changes of the mostly wide absorption bands. It is therefore necessary to evaluate these spectra with mathematical methods. These mathematical methods are based on chemometric software. Chemometry is to be understood as the application of mathematical methods in chemistry. The chemometric software in spectroscopy has the exercise of finding a statistical relationship between spectral data and the known property values of the samples used for calibration.